After learning they were hidden by a Royal insider beneath castle she expressed her fears they could have been lost forever.

The Queen said: "Did he remember where he put them..he might have died in the middle?"

After his conversation with the Queen, Bruce told the Times: "What was so lovely was that the Queen had no knowledge of it. Telling her seemed strangely odd.

"I think it’s gripping how personally involved George VI was and how secretive he was about it. I think like father, like daughter, this sense of how utterly important the crown jewels are to the country is very much felt by Elizabeth II."

In the documentary, the Queen also talks about the quirks of being head of state - from the perils of wearing a heavy crown to waling on a thick carpet pile.

She jokingly states you cannot look down when wearing the Imperial State Crown, which weighs 2lbs 13oz (1.28kgs), as your neck would “break”.

Looking at the crown, the Queen said: "Fortunately, my father and I have about the same sort of shaped head. But once you put it on, it stays. I mean, it just remains on."

Bruce said the head has to be kept still when wearing it and the Queen agreed: "Yes. And you can't look down to read the speech, you have to take the speech up. Because if you did your neck would break, it would fall off.

"So there are some disadvantages to crowns, but otherwise they're quite important things."

The crown jewels WW2 secret hiding place under a trap door at Windsor Castle is revealed in The Coronation documentary

The crown was made for George VI's coronation in 1937 and is set with 2,868 diamonds including 17 sapphires, 11 emeralds and hundreds of pearls, including four known as Queen Elizabeth I's earrings.

It also features a gemstone known as the Black Prince's Ruby, believed to have been worn by Henry V in his helmet at the Battle of Agincourt in 1415.

The documentary features footage of the Queen walking through the Abbey, and shows how her coronation dress was embroidered in silk with pearls, and gold and silver bullion thread.

"Well, I remember one moment when I was going against the pile of the carpet and I couldn't move at all," the Queen said.

The Queen talks about the Imperial State Crown in clip from The Coronation

Sacred oil used to anoint the Queen during her crowning was featured in a BBC documentary about her coronation as it was filmed for the first time.

The special oil is shown by Dr John Hall, Dean of Westminster during the programme.

Speaking about the oil, the Dean says in the programme, screened on Sunday: "It is kept very safe in the deanery, in a very hidden place in a little box here, which has in it a flask containing the oil from 1953.

"And it is not just olive oil, it's quite a complex mixture of different things."

The ingredients of the anointing oil are known but the exact recipe is not, and Dr Hall adds: "The composition of the oil was founded upon that used in the 17th century.

"Then you see what it consists of sesame seed and olive oil, perfume with roses, orange flowers, jasmine, musk, civet and ambergris."

The anointing of a new monarch is so sacred that it takes place under a canopy, transforming the moment into a deeply personal experience between the sovereign and God.

When the Queen was crowned on June 2 1953, live cameras filming the ceremony turned away during the symbolic moment.

The oil is stored in a bottle and traditionally held in great secrecy by the Dean of Westminster at the Abbey.

The Queen and Alastair Bruce watching archive footage of her carriage ride

During the ceremony it is kept in a solid gold flask called an ampulla - an artefact shaped like an eagle.

The Dean of Westminster plays an essential role in the lead-up to the coronation of a sovereign, and referring to the ceremony that saw the Queen crowned he says: "For six months, they closed the abbey.

"They laid a railway track down the centre of the abbey, bringing in tonnes and tonnes of wood and iron.

"I think there were 400 people in the choir and they were all up there. And there was an orchestra on the choir screen, 2,200 people can sit on the floor of the Abbey, 8,000 people were in here in 1953. They took a long time actually to get the whole thing ready."

During the documentary the Queen shares her memories of attending her father's coronation as an 11-year-old.

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